Ranked as the Marlins' top prospect by MLB.com and the best lefty prospect in the game, Heaney threw a perfect inning in a "B" game against the Cardinals on Wednesday on Field 2 at Roger Dean Stadium.

With his free and easy delivery, Heaney has arm action that's been called "effortless" by Marlins officials.

In his one inning on Wednesday, it was more of what the Marlins are becoming used to from Heaney, the 22-year-old who projects to open the season at Double-A Jacksonville. He has an outside chance to make the Opening Day rotation, but if he doesn't, he certainly could be in the big leagues some time this year.

Heaney's fastball maxed at 94 mph but was regularly at 93. He had one strikeout, on a fastball.

"It's not just stuff-wise with him," said Marty Scott, the Marlins' vice president of player development. "It's the intangibles, his mound presence. It's not arrogance. He doesn't show anybody up. It's just self-confidence, that he can put the ball where he wants to put it."

Heaney's velocity isn't necessarily overpowering, but his pitches have so much life.

"He doesn't throw any balls straight," Scott said. "He's got command, and he can control it. He's not afraid to pitch inside, to establish the plate. He's so meticulous with his work ethic and his game plan when he goes out there. It's almost like a surgeon. He's that precise in doing what he wants to do."